Depends on the place you want to go, the time of year you are there and the time of day you want to eat.
If it helps, Epcot's Guest Services (the one inside the park) has a message board that shows which restaurants have current availabilty. DHS has something similar near the board that shows the wait times. Don't know about MK or AK (AK only has two table service places anyway, three if you count Rainforest Cafe) but they have put a sign outside MK City Hall to notify guests when there is no table service dining available.